Plastic container closures and, more particularly, plastic closures for carbonated beverage bottles having threaded necks are well known, having previously been disclosed, for example, in U.S. Pat. Nos. 4,310,101; 4,326,639; 4,394,918; 4,461,391; and 4,476,987. Such closures typically employ sealing discs and/or molded flanges which contact the bottle lip to reduce the loss of carbonation. Used alone, integrally molded plastic flanges have not provided the desired sealing characteristics. Although sealing discs have proved to be quite effective for reducing loss of carbonation, they are usually separately manufactured and then inserted into a molded bottle cap, thereby increasing both the time and expense required to produce a satisfactory closure. A unitarily molded plastic bottle cap having satisfactory sealing characteristics is therefore needed, and such a closure is disclosed in U.S. Pat. No. 4,744,478.
In formulating compositions suitable for use in molding polymeric articles, many different factors must be considered. Such factors include, for example, the product configuration, the intended use, the use environment, whether or not the product will contact food or drink intended for human consumption, processing considerations, performance specifications, recyclability, and the like.
Compositions previously known and utilized by others for molding plastic closures for containers such as PET carbonated beverage bottles are not useful for producing closures having an integrally molded, foamed sealing layer as taught in the parent application. A new moldable, foamable, thermoplastic composition that is particularly suitable for molding such closures is therefore needed.